This invention relates to an oxidation resistant carbon-carbon composite and to a method for making such a composite including provision of a self-healing carbon-carbon fiber composite. "Carbon-carbon composites" as used herein should be understood to refer to fiber composites which include a carbon or graphite fiber impregnated with a carbon based resin such as phenolic. The composite is formed through a heating process during which volatiles therein are driven from the resin which is carbonized and graphitized. Hence a carbon-carbon composite remains, i.e. carbon fiber in a carbon matrix.
Presently the art of making and using carbon-carbon composite experiences difficulty in maintaining a long composite lifespan. Typically in an oxidizing medium at high temperatures such as during various heating applications, the carbon will react with oxygen to produce CO and CO.sub.2. The composite structurally breaks down and thus its use in various applications where heating is encountered such as in turbine engines, is limited and unreliable.
In an attempt to remedy this situation silicon based compounds such as silicon carbide have been infiltrated into the carbon-carbon composites porous fiber structure. When heated above a certain level silicon carbide reacts with the oxygen to provide a silicon oxide glass which is stable in the oxidizing medium. However, difficulty is still encountered because silicon carbide cracks during cycling through low temperature (e.g. approximately 1200.degree. F. regimes. Such cracks occur because silicon carbide and the carbon-carbon composite exhibit different coefficients of expansion. At temperatures above 2500.degree. F., the silicon oxide is typically in a liquid form with a sufficiently reduced viscosity in general to enter and seal the cracks. However, at lower temperatures, e.g. below 2500 F., such as occur in normal turbine cycling the viscosity of silicon oxide is too high to effectively seal the cracks. Oxygen eneters the cracks and the composite may be oxidized thereby losing approximately 10% or more of its weight per hour.